# coding:utf-8

class Node(object):
    def __init__(self, elem):
        self.elem = elem
        self.next = None


class SingleLinkList(object):
    def __init__(self, node=None):
        self.__head = node

    """单链表"""

    def is_empty(self):
        """判断链表是否为空"""
        return self.__head == None

    def length(self):
        cur = self.__head
        count = 0
        while cur != None:
            count += 1
            cur = cur.next
        return count

    def travel(self):
        """遍历整个链表"""
        cur = self.__head
        while cur != None:
            print("%s" % (cur.elem), end=" ")
            cur = cur.next
        print("")

    def add(self, item):
        """链表头部添加元素"""
        node = Node(item)
        node.next = self.__head
        self.__head = node

    def append(self, item):
        """链表尾部添加元素"""
        node = Node(item)
        if self.is_empty():
            self.__head = node
        else:
            cur = self.__head
            while cur.next != None:
                cur = cur.next
            cur.next = node

    def insert(self, pos, item):
        """指定位置添加元素"""
        if pos <= 0:
            self.add(item)
        elif pos > self.length() - 1:
            self.append(item)
        else:
            pre = self.__head
            count = 0
            while count < pos - 1:
                count += 1
                pre = pre.next
            node = Node(item)
            node.next = pre.next
            pre.next = node

    def remove(self, item):
        """删除节点"""
        cur = self.__head
        pre = None
        while cur!=None:
            if cur.elem == item:
                if cur == self.__head:
                    self.__head = cur.next
                else:
                    pre.next = cur.next
                print(item,"已经删除")
                return True
            else:
                pre = cur
                cur = cur.next
        print("不存在此节点",item)
        return False


    def search(self, item):
        """查找节点是否存在"""
        cur  = self.__head
        while cur != None:
            if cur.elem == item:
                return True
            else:
                cur = cur.next
        return False


if __name__ == '__main__':
    sll = SingleLinkList()
    print(sll.is_empty())
    print(sll.length())

    sll.append(1)
    print(sll.is_empty())
    print(sll.length())

    sll.add(8)
    sll.append(2)
    sll.append(3)
    sll.travel()
    sll.insert(-1,9)
    sll.travel()
    sll.insert(2,100)
    sll.travel()
    sll.insert(10,200)
    sll.travel()
    sll.remove(100)
    sll.travel()
    sll.remove(9)
    sll.travel()
    sll.remove(900)
    sll.remove(200)
    sll.travel()
    sll.remove(8)
    sll.travel()
    sll.remove(1)
    sll.remove(2)
    sll.travel()
    sll.remove(3)
    sll.travel()
    sll.remove(2000)
    sll.travel()